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/*
 * Copyright 1999-2017 Alibaba Group Holding Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package studio.raptor.sqlparser.visitor.functions;

import static studio.raptor.sqlparser.visitor.SQLEvalVisitor.EVAL_VALUE;

import studio.raptor.sqlparser.ast.SQLExpr;
import studio.raptor.sqlparser.ast.expr.SQLMethodInvokeExpr;
import studio.raptor.sqlparser.visitor.SQLEvalVisitor;

public class Concat implements Function {

  public final static Concat instance = new Concat();

  public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
    StringBuilder buf = new StringBuilder();

    for (SQLExpr item : x.getParameters()) {
      item.accept(visitor);

      Object itemValue = item.getAttributes().get(EVAL_VALUE);
      if (itemValue == null) {
        return null;
      }
      buf.append(itemValue.toString());
    }

    return buf.toString();
  }
}